Your smooth bore "buck & ball" gun has a lock that was sold by Henry Leman, but his factory did not build the gun. Leman made many types of firearms but also supplied parts to many local gunsmiths and retailers. Your gun's stock architecture, or shape, does not appear to be a Leman style. Rather, another gunsmith purchased a Leman percussion lock from his local hardware merchant and mounted it on this 1840s-1850s dual purpose gun. Its smooth bore could shoot both round ball for larger game, or shot for smaller game, thus the "buck & ball" designation. The rifle sights on the barrel show it could shoot round balls, while the round barrel and smooth bore are good indications it was also used with shot.
This type dual purpose gun is generally not as valuable as a rifle, and later half-stocked pieces are usually lower priced that full-stocked examples. Examples stocked in walnut usually bring less than those stocked in curly maple. If signed by the gunsmith on top of the barrel several inches behind the rear sight, it will help identify the gun and increase its value... but many of these plain, half-stocked buck & ball guns were rather generic pieces, a simple multi-purpose working gun for the farm. If unsigned, you will probably never know who made it. The gun is probably from Pennsylvania simply because more Leman locks were used there than in other state and the guard seems to suggest that origin. Values are subjective, but I would think it would fall in the $250-$350 range... and more if signed on the barrel so it can be assigned to a specific maker and location.
Shelby Gallien